Making bricks from clay is an age-old art that is practiced worldwide. Brick making ranges from ancient, entirely manual processes to modern, highly sophisticated, automated, mechanical processes. All of the processes involve mining a suitable shale or clay, crushing and/or grinding the mined material to an appropriate size, mixing the sized material with sufficient water to form a composition that is suitably plastic to form green brick (unfired brick), forming the green brick, drying the green brick and kiln firing the green brick to produce a finished brick. Modern processing has added machinery that not only eliminates the manual mixing of the brick composition but also extrudes the composition and cuts the extrusion into appropriate lengths.
In the practice of brick making the moisture content of the green brick is critical. A moisture content that is too high can cause low green strength, deformation during stacking, extended drying time and greater shrinkage during firing. A moisture content that is too low can cause insufficient plasticity for proper extrusion or, if successfully extruded, can result in a green brick without enough cohesiveness to withstand the rigors of processing so that it crumbles during further processing.